Auto biasing amps, worth every penny!
TUBE BIAS, socket to me!
BIAS: (I'm starting from zero understanding)
I have never measured/adjusted bias in the 3 tube amps, 3 tube receivers, and 2 tube preamps I have acquired over 47 years. I just switched my current Cayin from 6550's to KT88's. Adjust bias? Adjusters inside, scary electrocution warnings. I could pay someone else to do it, i.e. Steve at VAS 1 hr away in NJ, soooo,
What really counts? (personally I don't care about either heat or life, but would like to understand)
Heat?
Life?
Output stays Matched when adjusted?
Acoustic Performance?
_________?
Over the years, fronts off, bottoms off, I hose em down with contact cleaner/lubricant, compressed air, all controls and switchers, any adjusters, swish full spin back and forth. Kill any spiders, look for, replace the rare burnt resistor.
Then leave any adjusters (whatever they are) in the middle position, button it back up.
Two tube testers, my big hickock always agrees with small portable one, test strength, shorts, matched strength old and newly purchased. Large collection of NOS, used. Often used test essentially same strength as new ones.
When they go, it's usually a short.
I have never measured/adjusted bias in the 3 tube amps, 3 tube receivers, and 2 tube preamps I have acquired over 47 years. I just switched my current Cayin from 6550's to KT88's. Adjust bias? Adjusters inside, scary electrocution warnings. I could pay someone else to do it, i.e. Steve at VAS 1 hr away in NJ, soooo,
What really counts? (personally I don't care about either heat or life, but would like to understand)
Heat?
Life?
Output stays Matched when adjusted?
Acoustic Performance?
_________?
Over the years, fronts off, bottoms off, I hose em down with contact cleaner/lubricant, compressed air, all controls and switchers, any adjusters, swish full spin back and forth. Kill any spiders, look for, replace the rare burnt resistor.
Then leave any adjusters (whatever they are) in the middle position, button it back up.
Two tube testers, my big hickock always agrees with small portable one, test strength, shorts, matched strength old and newly purchased. Large collection of NOS, used. Often used test essentially same strength as new ones.
When they go, it's usually a short.
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- 91 posts total
vegasearsI wish my Cayin had it, alas, adjusters within. I got hooked on the reviews of the Cayin, they have auto-bias on mark 2,3 but my speakers are 16 ohm, only mark 1 has 16 ohm and it’s bias controls are inside. Seller had it biased just prior to sale to me, however that was for it’s 6550’s. I tried KT88’s for the first time, much prefer them, and .... of course I should bias them. I’m a DIY, but the words ’lethal’ ’death’ ... gave me lockstep. Made myself a nice long screwdriver out of a hardwood chopstick, dusted off 30 year old multimeter: new batteries, clean moving parts, pots, contacts, then realized, I never used this multimeter, I don’t understand this stuff. I even found it’s 30 year old manual in my ’instructions’ folder in the basement. I feel I’m all dressed up, nowhere to go. |
jss491,799 posts12-27-2020 12:08pmhttps://forums.stevehoffman.tv/threads/tube-integrated-with-autobias-equivalent-to-cayin-a88t.784890...Thanks, I am going back thru the discussion, reminding myself of the many suggestions, and took the time to go thru that, it is interesting. |
........................... thanks, finally had a look today. Preamp Connected??? "amp should be connected to your preamp but volume is turned fully down ( NO signal applied to the amp )." jomar I owned previously a A88T amp below are the biasing procedures. Please take note that the amp has HIGH voltages thus extra care should be taken. 1. Open bottom cover to have an access on the Test Point ( TP ) and Variable Trim pots (VR) . 2. Speakers should be connected and amp should be connected to your preamp but volume is turned fully down ( NO signal applied to the amp ). 3. Turn-ON power amp for about 10 minutes to warm-up tubes. 4. Attached positive ( Red ) probe of DVM (Digital Volt Meter) to Test Point . Negative probe of DVM to GROUND. 4. Adjust the VR which corresponds to the tube being biased to get 0.4Volts (400mV) reading *** VR1 for V5 , VR2 for V6, VR3 for V7 and VR4 for V8 5. Verify reading after 30 mins to finetune . 6. Power OFF amp and put back bottom cover |
- 91 posts total